Is it colour or color? Organise or organize? Neither is a mistake — they are regional standards, and the “error” your spell-checker flags is often just a dialect it was not set to expect. Knowing the main patterns lets you choose a variety deliberately and, most importantly, stick to it.
Why English spells the same word two ways
The differences are largely historical. As English spread and dictionaries were compiled on different continents, lexicographers made different choices about which older spellings to keep and which to simplify. American English adopted a number of streamlined forms; British English retained more of the older, often French- and Latin-influenced spellings; and other regions blended the two. None is more “correct” than another. What matters is matching your audience and being consistent within a single piece.
The main patterns to recognise
Most differences fall into a few tidy groups, which makes them easy to remember:
- -our vs -or: British colour, favour, honour, labour → American color, favor, honor, labor.
- -ise vs -ize: British writing often uses organise, realise, recognise, while American writing uses organize, realize, recognize. (Note that some British publishers use -ize too, so consistency matters more than the rule.)
- -re vs -er: British centre, theatre, metre, litre → American center, theater, meter, liter.
- -ce vs -se: British distinguishes the noun licence/practice from the verb license/practise; American English tends to use one spelling for both.
- Doubled consonants: British travelled, cancelling, modelled double the l; American traveled, canceling, modeled often do not.
Where Canadian and other Englishes sit
Canadian English is a genuine blend: it generally keeps British -our (colour, favour) but often prefers American -ize (organize), and mixes other choices word by word. Australian and other Commonwealth varieties lean British with their own local preferences. The practical lesson is that “British” and “American” are useful shorthands, not rigid boxes — when you write for a specific country, a regional dictionary such as an American dictionary or a British dictionary is the authority to follow.
It is not only spelling — vocabulary shifts too
Regional English differs in more than the letters within a word; sometimes the whole word changes. A British lift is an American elevator; a lorry is a truck; a flat is an apartment; autumn and fall name the same season. These are not spelling questions and no checker will flag them, but they signal your writing's origin as loudly as any -our ending. When you write for a particular audience, being aware of the vocabulary differences — not just the spellings — keeps your prose from reading as slightly foreign. You need not scrub every regionalism, but a word that will puzzle your reader is worth swapping for the one they use.
Setting your spell-checker to match
Most flags for these words are not spelling errors at all — they are a mismatch between your writing and the dictionary the checker uses. Set the language and region in your program to the variety you are writing (English (UK), English (US), English (Canada), and so on), and the false alarms disappear. If you switch between varieties for different audiences, get into the habit of checking the setting before you start, because a document half-checked against the wrong dictionary produces a confusing mix of real and phantom errors.
Consistency beats correctness
The one rule that outranks all the others: pick a variety and use it throughout. A document that writes colour in one paragraph and color in the next looks careless even though every word is correctly spelled. Decide up front which English you are using — usually your reader's — set your tools to match, and keep it uniform from title to sign-off. The same discipline applies when you are checking other languages, and it is a cornerstone of consistent, clear writing.